Non-Blockchain interoperability. Off-Chain & Middleware systems.
A way to facilitate interoperability between system is with off-chain or middleware systems.
Atomic Swaps.
Komodo
-Decentralized way to exchange two assets without going through a centralized exchange.
-Real life barter system.
(work on exchange of non-like protocols)
Oracles
Chainlink Oracles
-Can be used as a general purpose bridge between blockchains.
-Transactional activity of one blockchain can be used as an input trigger to an on-chain smart contract
-Oracles enable a wide range of cross-communication not possible in other models.
State Channels
-Method for swaping assets on the same blockchain is by creating an off-chain state channel to transfer assets
-Allows different parties to trade and record ownership
-On-chain transactions are reserved for final settlement.
-Scalable and beneficial for reducing on-chain transaction cost.
-State channels can be used to exchange messages about state changes before settling on-chain
Blockchain Operating System
Quant
-Patented protocol that runs on top of blockchains.
-Enables cross chain messaging and atomic swaps.
-Sandbox testing environments.
-Smartcontracts can be written in one language and deployed across many blockchains at the same time. (MAPPs)
-Contracts can be quickly adjusted to work on different platforms without needing rewrite.
For more information read Interoperability and Connectivity: Unlocking Smart Contracts 3.0